mkfs: drop support for zone != block

[minix.git] / libexec / ld.elf_so / symbol.c

/*      $NetBSD: symbol.c,v 1.54 2010/10/16 10:27:07 skrll Exp $         */

/*
 * Copyright 1996 John D. Polstra.
 * Copyright 1996 Matt Thomas <matt@3am-software.com>
 * Copyright 2002 Charles M. Hannum <root@ihack.net>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by John Polstra.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Dynamic linker for ELF.
 *
 * John Polstra <jdp@polstra.com>.
 */

#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: symbol.c,v 1.54 2010/10/16 10:27:07 skrll Exp $");
#endif /* not lint */

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/bitops.h>
#include <dirent.h>

#include "debug.h"
#include "rtld.h"

typedef void (*fptr_t)(void);

/*
 * If the given object is already in the donelist, return true.  Otherwise
 * add the object to the list and return false.
 */
static bool
_rtld_donelist_check(DoneList *dlp, const Obj_Entry *obj)
{
        unsigned int i;

        for (i = 0;  i < dlp->num_used;  i++)
                if (dlp->objs[i] == obj)
                        return true;
        /*
         * Our donelist allocation may not always be sufficient as we're not
         * thread safe. We'll handle it properly anyway.
         */
        if (dlp->num_used < dlp->num_alloc)
                dlp->objs[dlp->num_used++] = obj;
        return false;
}

static bool
_rtld_is_exported(const Elf_Sym *def)
{
        static const fptr_t _rtld_exports[] = {
                (fptr_t)dlopen,
                (fptr_t)dlclose,
                (fptr_t)dlsym,
                (fptr_t)dlerror,
                (fptr_t)dladdr,
                (fptr_t)dlinfo,
                (fptr_t)dl_iterate_phdr,
                NULL
        };
        int i;
        fptr_t value;

        value = (fptr_t)(_rtld_objself.relocbase + def->st_value);
        for (i = 0; _rtld_exports[i] != NULL; i++) {
                if (value == _rtld_exports[i])
                        return true;
        }
        return false;
}

/*
 * Hash function for symbol table lookup.  Don't even think about changing
 * this.  It is specified by the System V ABI.
 */
unsigned long
_rtld_elf_hash(const char *name)
{
        const unsigned char *p = (const unsigned char *) name;
        unsigned long   h = 0;
        unsigned long   g;
        unsigned long   c;

        for (; __predict_true((c = *p) != '\0'); p++) {
                h <<= 4;
                h += c;
                if ((g = h & 0xf0000000) != 0) {
                        h ^= g;
                        h ^= g >> 24;
                }
        }
        return (h);
}

const Elf_Sym *
_rtld_symlook_list(const char *name, unsigned long hash, const Objlist *objlist,
    const Obj_Entry **defobj_out, bool in_plt, DoneList *dlp)
{
        const Elf_Sym *symp;
        const Elf_Sym *def;
        const Obj_Entry *defobj;
        const Objlist_Entry *elm;
        
        def = NULL;
        defobj = NULL;
        SIMPLEQ_FOREACH(elm, objlist, link) {
                if (_rtld_donelist_check(dlp, elm->obj))
                        continue;
                rdbg(("search object %p (%s) for %s", elm->obj, elm->obj->path,
                    name));
                if ((symp = _rtld_symlook_obj(name, hash, elm->obj, in_plt))
                    != NULL) {
                        if ((def == NULL) ||
                            (ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
                                def = symp;
                                defobj = elm->obj;
                                if (ELF_ST_BIND(def->st_info) != STB_WEAK)
                                        break;
                        }
                }
        }
        if (def != NULL)
                *defobj_out = defobj;
        return def;
}

/*
 * Search the symbol table of a shared object and all objects needed by it for
 * a symbol of the given name. Search order is breadth-first. Returns a pointer
 * to the symbol, or NULL if no definition was found.
 */
const Elf_Sym *
_rtld_symlook_needed(const char *name, unsigned long hash,
    const Needed_Entry *needed, const Obj_Entry **defobj_out, bool inplt,
    DoneList *breadth, DoneList *depth)
{
        const Elf_Sym *def, *def_w;
        const Needed_Entry *n;
        const Obj_Entry *obj, *defobj, *defobj1;

        def = def_w = NULL;
        defobj = NULL;
        for (n = needed; n != NULL; n = n->next) {
                if ((obj = n->obj) == NULL)
                        continue;
                if (_rtld_donelist_check(breadth, obj))
                        continue;
                if ((def = _rtld_symlook_obj(name, hash, obj, inplt)) == NULL)
                        continue;
                defobj = obj;
                if (ELF_ST_BIND(def->st_info) != STB_WEAK) {
                        *defobj_out = defobj;

                        return (def);
                }
        }
        /*
         * Either the symbol definition has not been found in directly needed
         * objects, or the found symbol is weak.
         */
        for (n = needed; n != NULL; n = n->next) {
                if ((obj = n->obj) == NULL)
                        continue;
                if (_rtld_donelist_check(depth, obj))
                        continue;
                def_w = _rtld_symlook_needed(name, hash, obj->needed, &defobj1,
                    inplt, breadth, depth);
                if (def_w == NULL)
                        continue;
                if (def == NULL || ELF_ST_BIND(def_w->st_info) != STB_WEAK) {
                        def = def_w;
                        defobj = defobj1;
                        if (ELF_ST_BIND(def_w->st_info) != STB_WEAK)
                                break;
                }
        }
        if (def != NULL)
                *defobj_out = defobj;

        return def;
}

/*
 * Search the symbol table of a single shared object for a symbol of
 * the given name.  Returns a pointer to the symbol, or NULL if no
 * definition was found.
 *
 * The symbol's hash value is passed in for efficiency reasons; that
 * eliminates many recomputations of the hash value.
 */
const Elf_Sym *
_rtld_symlook_obj(const char *name, unsigned long hash,
    const Obj_Entry *obj, bool in_plt)
{
        unsigned long symnum;

        for (symnum = obj->buckets[fast_remainder32(hash, obj->nbuckets,
             obj->nbuckets_m, obj->nbuckets_s1, obj->nbuckets_s2)];
             symnum != ELF_SYM_UNDEFINED;
             symnum = obj->chains[symnum]) {
                const Elf_Sym  *symp;
                const char     *strp;

                assert(symnum < obj->nchains);
                symp = obj->symtab + symnum;
                strp = obj->strtab + symp->st_name;
                rdbg(("check \"%s\" vs \"%s\" in %p", name, strp, obj));
                if (name[1] == strp[1] && !strcmp(name, strp)) {
                        if (symp->st_shndx != SHN_UNDEF)
                                return symp;
#ifndef __mips__
                        /*
                         * XXX DANGER WILL ROBINSON!
                         * If we have a function pointer in the executable's
                         * data section, it points to the executable's PLT
                         * slot, and there is NO relocation emitted.  To make
                         * the function pointer comparable to function pointers
                         * in shared libraries, we must resolve data references
                         * in the libraries to point to PLT slots in the
                         * executable, if they exist.
                         */
                        else if (!in_plt && symp->st_value != 0 &&
                             ELF_ST_TYPE(symp->st_info) == STT_FUNC)
                                return symp;
#endif
                        else
                                return NULL;
                }
        }

        return NULL;
}

#ifdef COMBRELOC
static const Obj_Entry *_rtld_last_refobj;

/*
 * Called when an object is freed. Reset the cached symbol look up if
 * our last referencing or definition object just got unloaded.
 */
void
_rtld_combreloc_reset(const Obj_Entry *obj)
{
        if (_rtld_last_refobj == obj)
                _rtld_last_refobj = NULL;
}
#endif

/*
 * Given a symbol number in a referencing object, find the corresponding
 * definition of the symbol.  Returns a pointer to the symbol, or NULL if
 * no definition was found.  Returns a pointer to the Obj_Entry of the
 * defining object via the reference parameter DEFOBJ_OUT.
 */
const Elf_Sym *
_rtld_find_symdef(unsigned long symnum, const Obj_Entry *refobj,
    const Obj_Entry **defobj_out, bool in_plt)
{
        const Elf_Sym  *ref;
        const Elf_Sym  *def;
        const Obj_Entry *defobj;
        const char     *name;
        unsigned long   hash;

#ifdef COMBRELOC
        /*
         * COMBRELOC combines multiple reloc sections and sorts them to make
         * dynamic symbol lookup caching possible.
         *
         * So if the lookup we are doing is the same as the previous lookup
         * return the cached results.
         */
        static unsigned long last_symnum;
        static const Obj_Entry *last_defobj;
        static const Elf_Sym *last_def;

        if (symnum == last_symnum && refobj == _rtld_last_refobj
            && in_plt == false) {
                *defobj_out = last_defobj;
                return last_def;
        }
#endif

        ref = refobj->symtab + symnum;
        name = refobj->strtab + ref->st_name;

        /*
         * We don't have to do a full scale lookup if the symbol is local.
         * We know it will bind to the instance in this load module; to
         * which we already have a pointer (ie ref).
         */
        if (ELF_ST_BIND(ref->st_info) != STB_LOCAL) {
                if (ELF_ST_TYPE(ref->st_info) == STT_SECTION) {
                        _rtld_error("%s: Bogus symbol table entry %lu",
                            refobj->path, symnum);
                }

                hash = _rtld_elf_hash(name);
                defobj = NULL;
                def = _rtld_symlook_default(name, hash, refobj, &defobj, in_plt);
        } else {
                rdbg(("STB_LOCAL symbol %s in %s", name, refobj->path));
                def = ref;
                defobj = refobj;
        }
                
        /*
         * If we found no definition and the reference is weak, treat the
         * symbol as having the value zero.
         */
        if (def == NULL && ELF_ST_BIND(ref->st_info) == STB_WEAK) {
                rdbg(("  returning _rtld_sym_zero@_rtld_objself"));
                def = &_rtld_sym_zero;
                defobj = &_rtld_objself;
        }

        if (def != NULL) {
                *defobj_out = defobj;
#ifdef COMBRELOC
                if (in_plt == false) {
                        /*
                         * Cache the lookup arguments and results if this was
                         * non-PLT lookup.
                         */
                        last_symnum = symnum;
                        _rtld_last_refobj = refobj;
                        last_def = def;
                        last_defobj = defobj;
                }
#endif
        } else {
                rdbg(("lookup failed"));
                _rtld_error("%s: Undefined %ssymbol \"%s\" (symnum = %ld)",
                    refobj->path, in_plt ? "PLT " : "", name, symnum);
        }
        return def;
}

const Elf_Sym *
_rtld_find_plt_symdef(unsigned long symnum, const Obj_Entry *obj,
    const Obj_Entry **defobj, bool imm)
{
        const Elf_Sym  *def = _rtld_find_symdef(symnum, obj, defobj, true);
        if (__predict_false(def == NULL))
                return NULL;

        if (__predict_false(def == &_rtld_sym_zero)) {
                /* tp is set during lazy binding. */
                if (imm) {
                        const Elf_Sym   *ref = obj->symtab + symnum;
                        const char      *name = obj->strtab + ref->st_name;

                        _rtld_error(
                            "%s: Trying to call undefined weak symbol `%s'",
                            obj->path, name);
                        return NULL;
                }
        }
        return def;
}

/*
 * Given a symbol name in a referencing object, find the corresponding
 * definition of the symbol.  Returns a pointer to the symbol, or NULL if
 * no definition was found.  Returns a pointer to the Obj_Entry of the
 * defining object via the reference parameter DEFOBJ_OUT.
 */
const Elf_Sym *
_rtld_symlook_default(const char *name, unsigned long hash,
    const Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt)
{
        const Elf_Sym *def;
        const Elf_Sym *symp;
        const Obj_Entry *obj;
        const Obj_Entry *defobj;
        const Objlist_Entry *elm;
        def = NULL;
        defobj = NULL;
        DoneList donelist;

        _rtld_donelist_init(&donelist);

        /* Look first in the referencing object if linked symbolically. */
        if (refobj->symbolic && !_rtld_donelist_check(&donelist, refobj)) {
                rdbg(("search referencing object for %s", name));
                symp = _rtld_symlook_obj(name, hash, refobj, in_plt);
                if (symp != NULL) {
                        def = symp;
                        defobj = refobj;
                }
        }

        /* Search all objects loaded at program start up. */
        if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
                rdbg(("search _rtld_list_main for %s", name));
                symp = _rtld_symlook_list(name, hash, &_rtld_list_main, &obj,
                    in_plt, &donelist);
                if (symp != NULL &&
                    (def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
                        def = symp;
                        defobj = obj;
                }
        }

        /* Search all RTLD_GLOBAL objects. */
        if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
                rdbg(("search _rtld_list_global for %s", name));
                symp = _rtld_symlook_list(name, hash, &_rtld_list_global,
                    &obj, in_plt, &donelist);
                if (symp != NULL &&
                    (def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
                        def = symp;
                        defobj = obj;
                }
        }
        
        /* Search all dlopened DAGs containing the referencing object. */
        SIMPLEQ_FOREACH(elm, &refobj->dldags, link) {
                if (def != NULL && ELF_ST_BIND(def->st_info) != STB_WEAK)
                        break;
                rdbg(("search DAG with root %p (%s) for %s", elm->obj,
                    elm->obj->path, name));
                symp = _rtld_symlook_list(name, hash, &elm->obj->dagmembers,
                    &obj, in_plt, &donelist);
                if (symp != NULL &&
                    (def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
                        def = symp;
                        defobj = obj;
                }
        }

        /*
         * Search the dynamic linker itself, and possibly resolve the
         * symbol from there.  This is how the application links to
         * dynamic linker services such as dlopen.  Only the values listed
         * in the "_rtld_exports" array can be resolved from the dynamic
         * linker.
         */
        if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
                rdbg(("Search the dynamic linker itself."));
                symp = _rtld_symlook_obj(name, hash, &_rtld_objself, in_plt);
                if (symp != NULL && _rtld_is_exported(symp)) {
                        def = symp;
                        defobj = &_rtld_objself;
                }
        }

        if (def != NULL)
                *defobj_out = defobj;
        return def;
}